This research proposal involves the establishment and maintenance of a large colony of spontaneously hypertensive rats (SHR: Okamoto-Aoki strain) and their appropriate normotensive controls (Wistar and Wistar- Kyoto). This SHR strain is the best laboratory model thus far studied as a naturally-occurring and progressively developing hypertension for essential hypertensive man. We propose to develop methods for determining hemodynamic and myocardial functional changes during the course of this spontaneous hypertension and during the associated developing myocardial hypertrophy involving anesthetized as well as unanesthetized rats. These techniques will allow us to understand the natural history of the hemodynamic, physiological, and cardiovascular pharmacological characteristics of these SHR rats which distinguish them from their age and sex-matched normotensive (and, therefore, aging) counterparts. We also will relate these physiological alterations to pathologically-induced changes and compare these findings in the SHR rat with those observed in essential hypertensive man.